Strobe light photographing system

ABSTRACT

This disclosure relates to performing optimal strobe light emission control in accordance with the precision of distance information. This disclosure includes a photometry unit which measures light reflected by an object to be photographed by preliminary emission in a plurality of divided regions, an object distance detection unit, a distance precision determination unit (# 111  to # 117 ), a first calculation unit (# 121 ) which calculates a proper photometry level from an object distance detected by the object distance detection unit, a second calculation unit (# 121 ) which calculates an identification level for identifying an abnormal reflection region on the basis of the proper photometry level and a distance precision set in accordance with the determination result of the distance precision determination unit, a determination unit (# 121 ) which compares the photometry values of the plurality of regions with the identification level, thereby determining an abnormal reflection region, and a third calculation unit which calculates the photometry values of reflected object light in the plurality of regions from which the abnormal reflection region is excluded, wherein strobe light photographing is performed by controlling the main emission amount by the photometry values (# 124 ).

FIELD OF THE INVENTION

[0001] This invention relates to an improvement of a strobe lightphotographing system which causes a strobe light to preliminarily emitlight toward an object to be photographed, and calculates an mainemission amount for obtaining correct exposure.

BACKGROUND OF THE INVENTION

[0002] In automatic exposure photographing by adjusting light from astrobe light that is reflected by an object to be photographed, if anobject with high reflectance such as a glass or mirror exists on theobject side, exposure is adjusted to the high-reflectance object,resulting in underexposure of a principal object.

[0003] Japanese Patent Laid-Open No. 3-287240 discloses an automaticlight adjustment camera. More specifically, the strobe lightpreliminarily emits light immediately before photographing on theassumption that a principal object is located at an in-focus distance.Light reflected by the object is measured using a photometry sensorcapable of dividing the photographing region into a plurality of regionsand measuring light in each region. When the photometry result of agiven region is higher than the brightness at the photographingdistance, a high-reflectance object is determined to exist in thisregion. This region is excluded from the light adjustment region,eliminating the influence of regular reflection (high reflection).

[0004] The automatic light adjustment camera disclosed in patentreference 1 can prevent underexposure by excluding an abnormalreflection region corresponding to a high-reflectance object such as aglass facing the camera. However, an abnormal reflection region cannotbe accurately determined from, e.g., a lens having low distanceinformation precision (meaning the precision of information (distanceinformation) obtained by converting the position of a focusing lensafter focus adjustment into an object distance), or a short-focus lensthrough which the object distance cannot be accurately obtained as theobject distance becomes longer.

SUMMARY OF THE INVENTION

[0005] Accordingly, it is an object of the present invention to providea strobe light photographing system capable of performing preferablestrobe light emission control in accordance with the precision ofdistance information.

[0006] A exemplary system which includes a camera body, aninterchangeable lens mounted on the camera body, and a strobe lightmounted on the camera body, and performs preliminary emission beforemain emission in strobe light photographing, comprising: a unit whichhas a plurality of regions for splitting a field into a plurality offields and performing photometry, and measures light reflected by anobject to be photographed by preliminary emission in the plurality ofregions; a unit which detects distance information of the object from aposition of a focusing lens; a unit which determines precision of thedistance information; a unit which calculates a proper photometry levelfrom the distance information; a unit which calculates an identificationlevel for identifying an abnormal reflection region on the basis of theproper photometry level and a distance precision set in accordance witha determination result of the precision; a unit which comparesphotometry values of the plurality of regions or light adjustmentregions out of the plurality of regions with the identification level,thereby determining an abnormal reflection region; and a unit whichcontrols an main emission amount by photometry values of reflectedobject light in the plurality of regions or the light adjustment regionsout of the plurality of regions from which the abnormal reflectionregion is excluded.

[0007] The invention is particularly advantages since it can provide thestrobe light photographing system capable of performing optimal strobelight emission control in accordance with the precision of distanceinformation.

[0008] Other features and advantages of the present invention will beapparent from the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

[0010]FIG. 1 is a sectional view showing an illustrative strobe lightphotographing system including a single-lens reflex camera and a strobelight mounted on the camera according to an embodiment of the presentinvention;

[0011]FIG. 2 is a block diagram showing the illustrative circuitarrangement of the strobe light photographing system according to theembodiment of the present invention;

[0012]FIG. 3 is a view for explaining the arrangement of an illustrativephotometry sensor in the strobe light photographing system according tothe embodiment of the present invention;

[0013]FIG. 4 is a block diagram showing the illustrative circuitarrangement of a strobe light serving as a building component of thestrobe light photographing system according to the embodiment of thepresent invention;

[0014]FIG. 5 is a flow chart showing part of operation in a camera bodyserving as a building component of the strobe light photographing systemaccording to the embodiment of the present invention;

[0015]FIG. 6 is a flow chart showing operation subsequent to theoperation in FIG. 5;

[0016]FIG. 7 is a flow chart showing operation subsequent to theoperation in FIG. 6;

[0017]FIG. 8 is a table showing the contribution of object distanceinformation in the strobe light photographing system according to theembodiment of the present invention;

[0018]FIG. 9 is a view showing an example of an object influenced byabnormal reflection according to the embodiment of the presentinvention; and

[0019]FIG. 10 is a view for explaining the abnormal reflection regionand light adjustment region according to the embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Preferred embodiments of the present invention will now bedescribed in detail in accordance with the accompanying drawings.

[0021]FIG. 1 is a sectional view showing a strobe light photographingsystem including a single-lens reflex camera and a strobe light mountedon the camera according to an embodiment of the present invention. FIG.1 mainly shows an optical arrangement relationship.

[0022] In FIG. 1, reference numeral 1 denotes a camera body whose frontsurface is equipped with a photographing lens 11. The camera body 1incorporates optical components, mechanical components, electricalcircuits, an image sensing element (e.g., film or CCD), and the like.The camera body 1 can take a picture or photograph an image. Referencenumeral 2 denotes a main mirror which is obliquely inserted in aphotographing optical path in a viewfinder observation state, andretracted from the photographing optical path in a photographing state.The main mirror 2 is a half-mirror, and when it is obliquely inserted inthe photographing optical path, transmits almost half of rays from anobject to be photographed to a focus detection optical system (to bedescribed later).

[0023] Reference numeral 3 denotes a focusing screen which forms aviewfinder optical system and arranged on the prospective imaging planeof lenses 12 to 14 (to be described later). Reference numeral 4 denotesa pentaprism for changing the viewfinder optical path. Reference numeral5 denotes an eyepiece. The photographer sees the focusing screen 3through this window and can observe the photographing frame. Referencenumerals 6 and 7 denote an imaging lens and photometry sensor formeasuring the object brightness within the viewfinder observation frame.The imaging lens 6 is conjugate to the focusing screen 3 and photometrysensor 7 via a reflection optical path in the pentaprism 4.

[0024] Reference numeral 8 denotes a focal plane shutter. Referencenumeral 9 denotes a photosensitive member which is a silver halide filmor an image sensing element such as a CCD. Reference numeral 25 denotesa submirror which is obliquely inserted in the photographing opticalpath together with the main mirror 2 in the viewfinder observationstate, and retracted from the photographing optical path in thephotographing state. The submirror 25 deflects a ray having passedthrough the obliquely arranged main mirror 2, and guides the ray to thefocus detection unit (to be described later).

[0025] Reference numeral 26 denotes a focus detection unit which iscomprised of a secondary imaging mirror 27, a secondary imaging lens 28,a focus detection line sensor 29, a focus detection circuit (to bedescribed later), and the like. The secondary imaging mirror 27 andsecondary imaging lens 28 form a focus detection optical system, andform the secondary imaging plane of the photographing lens 11 on thefocus detection line sensor 29. The focus detection unit 26 detects thefocusing state of the photographing lens 11 by so-called phasedifference detection, and sends the detection result to an autofocusingdevice which controls the focusing mechanism of the photographing lens.

[0026] Reference numeral 10 denote mount contacts serving ascommunication interfaces between the camera body 1 and the photographinglens 11.

[0027] Of the lenses 12 to 14, the first lens group (to be also referredto as a focusing lens hereinafter) 12 moves back and forth on theoptical axis to adjust the focus position of the photographing frame.The second lens group 13 moves back and forth on the optical axis,changes the focal length of the photographing lens 11, and changes themagnification of the photographing frame. The lens 14 is a fixed thirdlens group. Reference numeral 15 denotes a stop. Reference numeral 16denotes a driving motor which is a focus driving motor for moving thefocusing lens 12 back and forth along the optical axis in autofocusingoperation. Reference numeral 17 denotes a stop driving motor forchanging the aperture diameter of the stop 15. Reference numeral 18denotes a distance encoder 1. A brush 19 attached to the focusing lens12 slides along with movement of the focusing lens 12. By utilizingthis, the distance encoder 18 reads the position of the focusing lens 12on the basis of the position of the brush 19, and generates a signalcorresponding to the object distance. That is, the distance encoder 18,the brush 19, and a lens microcomputer 112 (to be described later)constitute an object distance detection means which reads the positionof the focusing lens 12 after focusing and outputs a signal (objectdistance information) obtained by converting the position into an objectdistance.

[0028] Reference numeral 30 denotes a strobe light detachable from thecamera body 1. The strobe light 30 is mounted on the camera body 1, andcontrols emission in accordance with a signal from the camera body 1.Reference numeral 31 denotes a xenon tube (to be referred to as an Xetube hereinafter) which converts current energy into emission energy.Reference numerals 32 and 33 denote a reflecting plate and Fresnel lenswhich efficiently condense emission energy to an object to bephotographed. Reference numeral 37 denotes a glass fiber which guidespart of light emitted by the Xe tube 31 to a first light-receivingelement 38 such as a photodiode in order to monitor the emission amountof the Xe tube 31. The emission amounts of preliminary emission and mainemission of the Xe tube 31 can be monitored.

[0029] Reference numeral 35 denotes a second light-receiving elementsuch as a photodiode for monitoring light emitted by the Xe tube 31. Theemission current of the Xe tube 31 is limited by an output from thesecond light-receiving element 35, and flat emission is controlled.Reference numerals 34 and 36 denote light guides which are integratedwith the reflector 33, and respectively reflect part of light from theXe tube 31 to the second light-receiving element 35 and glass fiber 37.Reference numeral 39 denotes strobe light contacts serving ascommunication interfaces between the camera body 1 and the strobe light30.

[0030] The circuit arrangement of the strobe light photographing systemwill be explained with reference to FIG. 2. The same reference numeralsas in FIG. 1 denote the same parts.

[0031] A circuit arrangement in the camera body 1 will be described. Acamera microcomputer 100 is connected to a focus detection circuit 105,the photometry sensor 7, a shutter control circuit 107, a motor controlcircuit 108, a switch sensing circuit 110, and a liquid crystal displaycircuit 111. The camera microcomputer 100 transfers signals via themount contacts 10 to the lens control circuit 112 incorporated in thephotographing lens 11. The camera microcomputer 100 transfers signalsvia the strobe light contacts 39 to a strobe light microcomputer 200incorporated in the strobe light 30.

[0032] The focus detection circuit 105 performs storage control and readcontrol of the focus detection line sensor 29 in accordance with signalsfrom the camera microcomputer 100, and outputs pieces of pixelinformation to the camera microcomputer 100. The camera microcomputer100 A/D-converts these pieces of information, and detects a focusingstate by phase difference detection. The camera microcomputer 100exchanges signals with the lens microcomputer 112, and performs focusingcontrol of the photographing lens 11.

[0033] The photometry sensor 7 outputs brightness signals in a steadystate in which the strobe light 30 does not preliminarily emit lighttoward an object to be photographed and in a state in which the strobelight 30 preliminarily emits light. The camera microcomputer 100A/D-converts the brightness signals, calculates an F-number and shutterspeed before photographing exposure adjustment, and calculates theemission amount of the strobe light in exposure. At the same time, thecamera microcomputer 100 measures the color of the object, which will bedescribed later.

[0034] In accordance with signals from the camera microcomputer 100, theshutter control circuit 107 controls energization of a front shuttercurtain driving magnet MG-1 and rear shutter curtain driving magnet MG-2which form the focal plane shutter 8. The shutter control circuit 107operates the front and rear shutter curtains to perform exposureoperation. The motor control circuit 108 controls a motor M inaccordance with a signal from the camera microcomputer 100 to performup-down operation of the main mirror 2, shutter charge, and the like.

[0035] SW1 represents a switch which is turned on by the first stroke(half stroke) of a release button (not shown) and starts photometry andAF (Auto Focusing). SW2 represents a switch which is turned on by thesecond stroke (full stroke) of the release button and starts shutteroperation, i.e., exposure operation. SWFELK represents a switch whichindependently performs preliminary emission. The status signals ofswitches such as an ISO sensitivity setting switch, stop setting switch,and shutter speed setting switch which are operation members (notshown), in addition to the switches SW1, SW2, and SWFELK, are read bythe camera microcomputer 100 via the switch sensing circuit 110.

[0036] The liquid crystal display circuit 111 controls a viewfinderdisplay 24 and external display 42 in accordance with signals from thecamera microcomputer 100.

[0037] An electrical circuit arrangement in the photographing lens 11will be explained. The camera body 1 and photographing lens 11 areelectrically connected to each other via the lens mount contacts 10. Themount contacts 10 include a contact L0 serving as a power supply contactfor the focus driving motor 16 and stop driving motor 17 in thephotographing lens 11, a power supply contact L1 for the lensmicrocomputer 112, a clock contact L2 for serial data communication, acontact L3 for transmitting data from the camera body 1 to thephotographing lens 11, a contact L4 for transmitting data from thephotographing lens 11 to the camera body 1, a motor ground contact L5for a motor power supply, and a ground contact L6 for the power supplyof the lens microcomputer 112.

[0038] The lens microcomputer 112 is connected to the cameramicrocomputer 100 via the lens mount contacts 10. In accordance withsignals from the camera microcomputer 100, the lens microcomputer 112operates the focus driving motor 16 for driving the focusing lens 12 andthe stop driving motor 17 for driving the stop 15, adjusts the focus ofthe photographing lens 11, and controls the stop. Reference numerals 50and 51 denote a photodetector and pulse plate. The lens microcomputer112 counts the number of pulses to obtain position information of thefocusing lens 12 in focusing (focusing operation). As a result, thefocus of the photographing lens 11 can be adjusted. Position informationof the focusing lens 12 read by the distance encoder 18 is input to thelens microcomputer 112. The lens microcomputer 112 converts the positioninformation into object distance information, and transfers the objectdistance information to the camera microcomputer 100.

[0039] The photometry sensor 7 will be described with reference to FIG.3. The photometry sensor 7 is an integrated circuit comprised oflight-receiving elements such as silicon photodiodes, and an amplifierwhich amplifies a photocurrent generated by the light-receivingelements. FIG. 3 shows the light-receiving portions of the photometrysensor 7 when viewed from the incident surface.

[0040] The light-receiving portions of the photometry sensor 7 are soarranged as to receive light from almost the same range as the frame ofan image sensing element or film 7. The light-receiving surface isdivided into a plurality of regions P(0,0) to P(6,4) in FIG. 3. Thenumber of regions coincides with the number of light-receiving portions(35 in this example). Each light-receiving portion is a light-receivingelement such as a silicon photodiode, and when light impinges on it,generates a predetermined photocurrent. Photocurrent outputs aresupplied to the camera microcomputer 100 sequentially from an upper leftlight-receiving element to a lower right light-receiving element via aknown logarithmic compression amplifier. The camera microcomputer 100A/D-converts outputs from the light-receiving elements, and can measurethe brightness values of the portions within the photographing range asdigital values.

[0041] The arrangement of the strobe light 30 will be described withreference to FIG. 4. In FIG. 4, the strobe light microcomputer 200controls the overall operation of the strobe light 30. Reference numeral201 denotes a power supply battery. Reference numeral 202 denotes aDC/DC converter which boosts the battery voltage to several hundred V.Reference numeral 203 denotes a main capacitor which stores emissionenergy. Reference numerals 204 and 205 denote resistors which divide thevoltage of the main capacitor 203 at a predetermined ratio. Referencenumeral 206 denotes a coil for limiting an emission current. Referencenumeral 207 denotes a diode for absorbing a counterelectromotive voltagegenerated when emission is stopped. The xenon tube 31 is an Xe tube.Reference numeral 211 denotes a trigger generation circuit. Referencenumeral 212 denotes an emission control circuit such as an IGBT.

[0042] Reference numeral 230 denotes a data selector which selects D0,D1, or D2 by a combination of two inputs Y0 and Y1 and outputs theselected signal to Y. Reference numeral 231 denotes a comparator forcontrolling the emission level of flat emission. Reference numeral 232denotes a comparator for controlling the emission amount in flashemission (strobe light emission). The second light-receiving element 35such as a photodiode is a light-receiving sensor for controlling flatemission, and monitors an optical output from the Xe tube 31. Referencenumeral 234 denotes a photometry circuit which amplifies a small currentflowing through the second light-receiving element 35 and converts thephotocurrent into a voltage. The first light-receiving element 38 suchas a photodiode is a light-receiving sensor for controlling flashemission, and monitors an optical output from the Xe tube 31. Referencenumeral 236 denotes an integrating circuit for logarithmicallycompressing a photocurrent flowing through the first light-receivingelement 38, and compressing and integrating the emission amount of theXe tube 31.

[0043] The strobe light contacts 39 are arranged at a hot shoe in orderto communicate with the camera body 1. Reference numeral 242 denotes apower switch for switching the strobe light 30 between power-on andpower-off states.

[0044] The main terminals of the strobe light microcomputer 200 will beexplained. CNT represents a control output terminal which controlscharting of the DC/DC converter 202. COM2 represents a control outputterminal corresponding to the ground potential of the switch 242. OFFrepresents an input terminal which is selected when the strobe light 30is OFF. ON represents an input terminal which is selected when thestrobe light 30 is ON. CK represents a sync clock input terminal forserial communication with the camera body 1. DO represents a serialoutput terminal for transferring serial data from the strobe light 30 tothe camera body 1 in synchronism with a sync clock. DI represents aserial data input terminal for transferring serial data from the camerabody 1 to the strobe light 30 in synchronism with a sync clock. CHGrepresents an output terminal which transmits as a current to the camerawhether the strobe light can emit light, which is determined from thevoltage of the main capacitor 203. X represents an input terminal for anemission start signal at the X contact of the camera. GND represents aground contact.

[0045] INT represents the integral control output terminal of theintegrating circuit 236. AD0 represents an A/D conversion input terminalfor reading an integral voltage representing the emission amount of theintegrating circuit 236. DA0 represents a D/A output terminal foroutputting the comparison voltages of the comparators 231 and 232. Y0and Y1 represent output terminals for the selection state of the dataselector 230. YIN represents an input terminal for monitoring the outputstate of the data selector 230. TRIG represents an output terminal foran emission trigger. AD1 represents an A/D input terminal for monitoringthe voltage of the main capacitor 203 via the voltage-dividing resistors204 and 205.

[0046] The operation of the strobe light photographing system having theabove arrangement will be explained with reference to the flow charts ofFIGS. 5 and 6.

[0047] When the switch SW1 of the camera body 1 shown in FIG. 2 isturned on, the operation starts in step #100. The camera microcomputer100 detects the focus by a known method from a shift of an object imageformed on the focus detection line sensor 29 within the focus detectionunit 26 including the focus detection circuit 105. The cameramicrocomputer 100 calculates a lens driving amount to an in-focusposition, and outputs the calculated lens driving amount to the lensmicrocomputer 112 via the serial communication lines LCK, LDO, and LDI.Upon reception of the lens driving amount, the lens microcomputer 112drives the focus driving motor 16, and reads from the photodetector 50rotation of the pulse plate 51 directly connected to the focus drivingmotor 16. If the focus driving motor 16 is driven by the designateddriving amount, the lens microcomputer 112 stops the focus driving motor16.

[0048] At the end of focusing operation, the flow advances to step #101.The camera microcomputer 100 instructs the photometry sensor 7 tomeasure brightness values Ba(0,0) to Ba(6,4) of ordinary light in theplurality of divided regions P(0,0) to P(6,4). The photometry result islogarithmically compressed by the logarithmic compression amplifier (notshown) in the photometry sensor 7, the logarithmic compression result isconverted into a voltage value, and the voltage value is input to thecamera microcomputer 100. The camera microcomputer 100 sequentiallyreads P(0,0) to P(6,4) via the A/D input terminals, adds full-apertureFNo(Avo) and aperture value correction (Avc) of the photographing lens11, and stores the results as brightness data Bva(0,0) to BVa(6,4) ofthe respective portions in the internal RAM (not shown) of the cameramicrocomputer 100.

[0049] In step #102, the camera microcomputer 100 determines an exposurevalue (BVs) by a known method from the brightness values BVa(0,0) toBVa(6,4) in the measured regions. The camera microcomputer 100determines a time value (TV) and aperture value (AV) in accordance witha set camera photographing mode.

[0050] In step #103, the TV value and AV value determined in step #102are displayed on the viewfinder display 24 and external display 42. Ifthe photographing start switch SW2 is ON in step #104, the flow advancesto step #105; if OFF, returns to step #101.

[0051] In step #105, the camera microcomputer 100 instructs the strobelight microcomputer 200 on preliminary (pre) emission by serialcommunication via communication terminals S0, S1, and S2. Upon receptionof this preliminary emission instruction, the strobe light microcomputer200 performs preliminary emission operation at a predetermined lightquantity.

[0052] Preliminary emission operation will be explained. The strobelight microcomputer 200 sets a predetermined voltage at the DA0 terminalin accordance with a predetermined emission level designated by thecamera body 1. The strobe light microcomputer 200 outputs Hi and Lo toY1 and Y0 to select the input D2. At this time, the Xe tube 31 has notemitted light yet, almost no photocurrent of the first light-receivingelement 38 flows, and no output from the monitor circuit 234 to theinverting input terminal of the comparator 231 is generated. Hence, theoutput of the comparator 231 is Hi, and the emission control circuit 212is turned on.

[0053] When a trigger signal is output from the TRIG terminal, thetrigger generation circuit 211 excites the Xe tube 31 which hasgenerated a high voltage, starting preliminary emission.

[0054] The strobe light microcomputer 200 instructs the integratingcircuit 236 to start integration. The integrating circuit 236 which hasreceived this instruction starts integrating an output from the monitorcircuit 234, i.e., a logarithmically compressed photoelectric outputfrom the first light-receiving element 38. At the same time, a timerwhich counts the emission time is activated.

[0055] After the start of preliminary emission, a photocurrent from thesecond light-receiving element 35 for controlling the emission level offlat emission increases, and an output from the monitor circuit 234increases. When an output from the monitor circuit 234 becomes higherthan a predetermined comparison voltage set at the non-inverting inputof the comparator 231, an output from the comparator 231 is inverted toLo, and the emission control circuit 212 cuts off the emission currentof the Xe tube 31. Accordingly, the discharge loop is disconnected, buta flow-back loop is formed by the diode 207 and coil 206. Afterovershooting by a circuit delay settles, the emission current graduallydecreases.

[0056] The emission level drops along with the decrease in emissioncurrent, the photocurrent of the second light-receiving element 35decreases, and an output from the monitor circuit 234 also decreases.When the level reaches a predetermined comparison level, an output fromthe comparator 231 is inverted to Hi again, and the emission controlcircuit 212 is turned on again. The discharge loop of the Xe tube 31 isformed, the emission current increases, and the emission level alsorises.

[0057] In this manner, the comparator 231 repetitively increases anddecreases the emission level within a short cycle by using as a center apredetermined comparison voltage set at DA0. Consequently, flat emissionin which emission continues at an almost constant desired emissionlevel.

[0058] When the timer counts the lapse of a predetermined emission time,the strobe light microcomputer 200 sets Lo at the Y1 and Y0 terminals.In response to this, the input D0, i.e., Lo-level input of the dataselector 230 is selected, and the output forcibly changes to Lo level.The emission control circuit 212 disconnects the discharge loop of theXe tube 31, thereby ending preliminary emission (flat emission).

[0059] At the end of emission, the strobe light microcomputer 200 readsfrom the A/D input terminal AD0 an output from the integrating circuit236 which integrates the preliminary emission amount, and A/D-convertsthe output, reading the integral value, i.e., the emission amount inpreliminary emission as a digital value.

[0060] At the end of preliminary emission, the flow advances to step#106. Reflected object light by preliminary emission is received by thephotometry sensor 7 of the camera body 1 via the photographing lens 11.Reflected object light in preliminary emission is calculated for eachblock by the same method as step #101, measuring object brightnessvalues BVf(0,0) to BVf(6,4) by reflected light from the strobe light.

[0061] The flow advances to step #107. The camera microcomputer 100subtracts an object brightness BVa(x,y) by natural light obtained instep #101 from an object brightness BVf(x,y) in preliminary emission,and extracts only a brightness value dF(x,y) of only reflected light bypreliminary emission.

[0062] In step #108, the photometry value of reflected object light thatcorresponds to a focus detection point (meaning a region where defocusinformation is detected) is calculated. For descriptive convenience, inthe first embodiment, the focus detection point is set to the center(P(3,2) in FIG. 3) of the 35-division photometry sensor 7, the lightadjustment area is set to 3×3 regions centered at P(3,2), and theaverage value of these regions is defined as a photometry value. Thatis, an average photometry value dFave of reflected object light is givenfrom the values dF(x,y) of the regions of the photometry sensor 7obtained in step #107:

dFave=(dF(2,1),+dF(3,1)+dF(4,1)+dF(2,2)+dF(3,2)+dF(4,2)+dF(2,3)+dF(3,3)+dF(4,3))/9

[0063] In this example, the values dF(x,y) are uniformly averaged.Alternatively, the values dF(x,y) may be averaged by setting the weightof the focus detection region relatively high and the value of theperipheral region relatively low.

[0064] In step #110, whether the lens has object distance information(to be also simply referred to as distance information hereinafter) isdetermined from a status determination signal from the photographinglens 11. If YES in step #110, the flow advances to step #111; if NO, tostep #115. The status determination signal of the lens is informationacquired from the photographing lens by serial communication between thecamera and the lens.

[0065] If the lens is determined to have distance information and theflow advances to step #111, whether the lens has distance precisioninformation contained in the status determination signal is determined.If YES in step #111, the flow advances to step #112; if NO, to step#116.

[0066] In step #112, since the lens has both the distance informationand distance precision information, the flow branches to any one ofsteps #113, #114, and #115 in accordance with the acquired precisioninformation. If the lens is identified from the acquired precisioninformation to be a new model in which focusing division has a precisionof 0.5 to the distance apex value (DV), the lens is classified to class1 (#113). If the lens is identified to be an old model in which focusingdivision has a precision of 1.0 to the distance apex value (DV), thelens is classified to class 2 (#114). If focusing division does not haveany precision of even 1 to the distance apex value (DV), the lens isclassified to a lens having no distance information (#115). If the flowadvances to step #113 or #114, it advances to step #120; if the flowadvances to #115, to step #125.

[0067] For a lens having distance information but no distance precisioninformation, the flow advances from step #111 to step #116, and a lensidentification code (ID code: value different between lens models) isread from the photographing lens 11 by serial communication between thecamera and the lens. In step #117, the flow branches in accordance withthe lens identification code acquired from the photographing lens instep #116. For example, the flow advances to step #115 for a lens whosedistance information cannot be used for the precision, step #113 for alens corresponding to class 1, and step #114 for a lens corresponding toclass 2.

[0068] In step #118, object distance information is read from thephotographing lens 11 by serial communication between the camera and thelens. In step #119, the distance information range precision iscalculated from the distance information acquired in step #118:

Distance range precision=2*log 2(infinity distance/minimum objectdistance)

[0069] For example,

[0070] Infinity distance: 235 cm

[0071] Minimum object distance: 199 cm $\begin{matrix}{{Precision} = {2*\log \quad 2\quad \left( {{infinity}\quad {{distance}/{minimum}}\quad {object}\quad {distance}} \right)}} \\{= {2*\log \quad 2\quad \left( {235/199} \right)}} \\{= {0.48\quad ({EV})}}\end{matrix}$

[0072] In step #120, the class determined in step #113 or #114 iscorrected on the basis of the precision determined from the infinitydistance information and minimum object distance information in #119 inorder to decide the determination level of the abnormal reflectionregion. Class 1 has a precision of 0.5, and class 2 has a precision of1.0. The precision in an actual distance zone is given priority tofinally decide the class. That is, when even a lens of class 1 with aprecision of 0.5 has only a precision of 1 in a region close toinfinity, this lens is treated as a lens of class 2. A determinationlevel LVL0 is read out from a table in FIG. 8 representing thedetermination level on the basis of the finally determined class andobject distance information. In FIG. 8, object distance information isobtained by dividing by the focal length the infinity focal length ofthe photographing lens 11 that is read in step #118.

[0073] In step #121, a photometry level LVL1 for correct exposure isgiven by

LVL 1=PRG−log 2(infinity distance)+K

[0074] PRG: pre-emission guide number

[0075] K: constant

[0076] A determination level LVL2 for determining an abnormal reflectionregion is given by

LVL 2=LVL 1+LVL 0

[0077] A region where the photometry value is higher than the sum of thephotometry level LVL1 for correct exposure and the abnormal reflectiondetermination level LVL2 is excluded as an abnormal reflection regionfrom the light adjustment region. That is, the photometry values dF(0,0)to dF(6,4) of reflected object light in the regions of the photometrysensor 7 that are obtained in step #107 are compared with LVL2, and if aphotometry value is larger than LVL2, this sensor area is determined asan ineffective area (exclusion region).

[0078] In step #122, if the level of the exclusion region is equal to orhigher than a predetermined value, i.e., most of the frame is determinedto be an abnormal reflection region, the flow advances to step #124; ifNO, to step #123.

[0079] If most of the frame is determined not to be an abnormalreflection region and the flow advances to step #123, the photometryvalue dF is calculated from the remaining regions after exclusion:

dF=SUM(dFs of effective regions)/the number of effective regions

[0080]FIGS. 9 and 10 show an example for an actual object. Regionsindicated by dotted lines in FIG. 9 are divided photometry regions shownin FIG. 3. An area (P(1,1) to P(2,2)) surrounded by a bold line in FIG.10 is a region where the photometry value dF(x,y) of reflected light ishigher than the abnormal reflection region determination level LVL2obtained in step #121. This region is therefore excluded from the lightadjustment target. A region (P(2,1) to P(4,3)) surrounded by a bolddotted line is a light adjustment range when the focus detection pointis set to the center (P(3,2)). When the average value of reflectedobject light is calculated from the light adjustment range, the abnormalreflection regions P(2,1) and P(2,2) are excluded, preventingunderexposure of the principal object due to the abnormal reflectionregions.

[0081] If most of the frame is determined in step #122 to be an abnormalreflection region, the flow advances to step #124. In this case, lightadjustment using only the remaining regions results in a large error.Thus, the proper photometry level LVL1 calculated in step #121 is usedas the photometry value dF.

dF=LVL1

[0082] If no distance information is used, the flow advances from step#115 to step #125, and the levels of the regions are averaged inaccordance with the focus detection point to calculate the photometryvalue dF. That is, when the focus detection point is P(3,2) at thecenter of the frame,

dF=SUM(P(2,1) to P(4,3))/9

[0083] After that, the flow advances to step #126 to obtain an mainemission amount γ.

[0084] In step #120, object distance information is read from thephotographing lens 11 by serial communication between the camera and thelens. In the embodiment, the infinity distance and minimum objectdistance of the zone are read from the lens zone encoder (distanceencoder 18). In step #121, proper photometry level (LVL0) is obtainedfrom the infinity distance information and minimum object distanceinformation acquired in step #120 on the assumption that the object hasthe standard reflectance (22%):

LVL 0 F=PRG−log 2(infinity distance)+K

LVL 0 N=PRG−log 2(minimum object distance)+K

LVL 0=(LVL 0 F+LVL 0 N)/2

[0085] PRG: preliminary emission guide number

[0086] K: constant

[0087] In step #122, a contribution DVK is determined in accordance withthe distance precision and object distance.

[0088]FIG. 8 is a table showing numeric values which are stored in theinternal ROM of the camera microcomputer 100 in order to determine acontribution corresponding to the distance precision and objectdistance. In FIG. 8, the distance precision corresponds to class 1 andclass 2. The contribution is acquired from the table of FIG. 8 inaccordance with the distance precision class and a value obtained bydividing object distance information acquired in step #120 by the focallength (f) of the photographing lens 11. As the distance becomes longer,it cannot be accurately measured (error increases). A contributioncorresponding to the distance information precision and distanceinformation is therefore acquired from the table of FIG. 8.

[0089] In step #123, a photometry value dFtave which considers thecontribution (DVK) is calculated on the basis of the photometry valuedFave of the reflected object light component obtained in step #108 asthe photometry value of reflected object light by preliminary emission:

dFtave=dFave*(1−DVK)+LVL 0*DVK

[0090] DVK: contribution

[0091] In step #124, whether the difference between the photometry valuedFtave obtained in step #123 and the photometry value dFave of thereflected object light component obtained in step #108 is equal to orsmaller than a predetermined value (e.g., 0.5) is determined. If YES instep #124, the flow directly advances to step #126 without employing thephotometry value dFtave which considers the contribution calculated fromthe distance information; if NO, to #125 because the photometry valuedFtave which considers the contribution is used.

[0092] When the photometry value dFtave which considers the contributionand the photometry value dFave of only reflected object light are equalto or smaller than the predetermined value, the photometry value whichconsiders the contribution is not employed to prevent variations instrobe light exposure due to an autofocus detection error uponphotographing the same object at the same distance.

[0093] If the photometry value dFtave which considers the contributioncalculated from the distance information in step #123 is used, the flowadvances to step #125. In order to validate the distance information,dFtave calculated in step #123 replaces dFave (dF=dFt).

[0094] In step #126, an main emission amount γ of a final lightadjustment area is calculated in each region of the 35-divisionphotometry sensor 7:

γ=BVt−dFave

[0095] Note that BVt is calculated from the TV value and AV valueobtained in step #102:

BVt=TV+AV−SV

[0096] SV: speed value

[0097] In step #127, the camera microcomputer 100 instructs the strobelight microcomputer 200 on the calculated main emission amount γ via thecommunication terminals S0, S1, and S2 by serial communication. The flowthen advances to step #130.

[0098] In step #130, whether the shutter speed is equal to or lower thanthe tuning speed is determined. If the shutter speed is equal to orlower than the tuning speed, the flow advances to #131, and the cameramicrocomputer 100 transmits a flash emission mode to the strobe lightmicrocomputer 200. If the shutter speed is higher than the tuning speed,the flow advances to step #132, and the camera microcomputer 100transmits a flat emission mode and flat emission time (time obtained byadding the curtain speed to the shutter speed) to the strobe lightmicrocomputer 200.

[0099] In step #133, the main mirror 2 is moved up and retracted fromthe photographing optical path. At the same time, the cameramicrocomputer 100 instructs the lens microcomputer 112 to narrow downthe stop 15. In step #134, the flow waits until the main mirror 2completely retracts from the photographing optical path. After the mainmirror 2 completely retracts from the photographing optical path, theflow advances to step #135, and the camera microcomputer 100 energizesthe front shutter curtain driving magnet MG-1 to start opening the focalplane shutter 8.

[0100] In step #136, whether the emission mode is the flat (FP) emissionmode is determined. For the flat emission mode, the flow advances tostep #138. For the flash emission mode, the flow advances to step #137,and waits until the front curtain of the focal plane shutter 8 iscompletely opened and power is supplied to an X contact represented bySWX in FIG. 2. After that, the flow advances to step #138.

[0101] In step #138, the strobe light microcomputer 200 performs mainemission control corresponding to the emission mode designated by thecamera microcomputer 100. That is, the strobe light microcomputer 200performs flat emission control for the flat emission mode, and flashemission control for the flash emission mode.

[0102] Flash emission control will be explained. Flash emission controlis done when the camera shutter speed is equal to or lower than thetuning speed of the strobe light. In this case, the strobe lightmicrocomputer 200 outputs to the DA0 terminal a control voltagecorresponding to a set manual emission amount. This voltage is obtainedby adding a control voltage corresponding to the light quantitydifference between preliminary emission and main emission to the outputvoltage, i.e., integral voltage of the integrating circuit 236 which hasbeen described in preliminary emission.

[0103] For example, let V1 be the integral voltage upon preliminaryemission at a light quantity which is {fraction (1/32)} of the fullemission amount. For the same main emission amount of {fraction (1/32)},emission is stopped when the voltage reaches the same integral voltage.Thus, V1 is set as the comparison voltage of the comparator 232.Similarly, for an main emission amount of {fraction (1/16)}, emission isstopped when the voltage reaches an interval voltage larger by one stepthan that in preliminary emission. A voltage corresponding to one stepis added to the integral voltage in preliminary emission, and theresultant voltage is set as the comparison voltage of the comparator232.

[0104] The strobe light microcomputer 200 outputs “0 and 1” to the Y1and Y0 terminals, and selects the flash emission control comparator 232connected to the D1 input of the data selector 230. At this time, the Xetube 31 has not emitted light yet, and almost no photocurrent flowsthrough the first light-receiving element 38. The integrating circuit236 does not generate any output, and the −input voltage of thecomparator 232 is lower than that at the +input terminal. Hence, theoutput voltage of the comparator 232 changes to high level, and theemission control circuit 212 is turned on. At the same time, the strobelight microcomputer 200 outputs a Hi signal for a predetermined timefrom the TRIG terminal. The trigger circuit 211 generates a high triggervoltage. Upon application of a high voltage to the trigger electrode ofthe Xe tube 31, the Xe tube 31 starts emitting light.

[0105] After the Xe tube 31 starts emitting light, a photocurrent flowsthrough the first light-receiving element 38, and an output from theintegrating circuit 236 increases to a predetermined voltage set at the+input terminal of the comparator 232. The comparator 232 is theninverted, its output voltage changes to low level, and the emissioncontrol circuit 212 is turned off, stopping emission.

[0106] At this time, the Xe tube 31 has generated a predeterminedemission amount and stops emission, obtaining a desired light quantitynecessary for strobe light photographing.

[0107] Flat emission control will be explained. Flat emission control isdone when the camera shutter speed is higher than the tuning speed ofthe strobe light. The strobe light microcomputer 200 outputs to the DA0terminal a control voltage corresponding to a set manual flat emissionamount. This voltage is obtained by adding a control voltagecorresponding to the light quantity difference between preliminaryemission and main emission to a voltage set as the comparison voltage ofthe comparator 231 in preliminary emission.

[0108] For example, let V1 be the control voltage upon preliminaryemission at a light quantity which is {fraction (1/32)} of the fullemission amount. In emission at the same main emission amount of{fraction (1/32)}, flat emission control suffices to be executed at thesame control voltage. Thus, V1 is set as the comparison voltage of thecomparator 231. Similarly, for an main emission amount of {fraction(1/16)}, the control voltage is set larger by one step than that inpreliminary emission. A voltage corresponding to one step is added tothe integral voltage in preliminary emission, and the resultant voltageis set as the comparison voltage of the comparator 232.

[0109] The strobe light microcomputer 200 outputs “1 and 0” to the Y1and Y0 terminals, and selects the flat emission control comparator 231connected to the D2 input of the data selector 230. Thereafter, flatemission is performed by the same operation as the above-describedpreliminary emission operation. Upon the lapse of a predetermined timedesignated by the camera microcomputer 100, the Y1 and Y0 terminals ofthe strobe light microcomputer 200 are set to “0 and 0”, ending emissionprocessing.

[0110] Referring back to FIG. 7, the flow advances to step #139 upon thelapse of a predetermined full-aperture shutter time. The cameramicrocomputer 100 energizes the rear shutter curtain driving magnetMG-2, and closes the rear curtain of the focal plane shutter 8, endingexposure. When the emission mode is flat emission, emission continuesuntil the rear curtain is completely closed. After the end of a seriesof photographing sequences, the flow advances to step #140 to move downthe main mirror 2 and end photographing.

[0111] According to the above embodiment, the strobe light photographingsystem comprises a means (step #108 in FIG. 5) for calculating firstphotometry data (dFave) obtained by the photometry sensor 7 (morespecifically, 3×3 regions including a focus detection point out of 35regions having undergone photometry) which measures light reflected byan object in preliminary emission, a means (distance encoder 18, brush19, and lens microcomputer 112) for detecting object distanceinformation, a means (step #121 in FIG. 6) for calculating proper secondphotometry data (LVL0) on the basis of the object distance information,a means (steps #122 and #123 in FIG. 6) for calculating third photometrydata (dFtave) from the first photometry data, the second photometrydata, and a contribution (DVK) corresponding to the distance informationand distance precision, and a means (steps #124 to #126 in FIG. 6) forcontrolling an main emission amount on the basis of the third photometrydata and performing strobe light photographing.

[0112] That is, the third photometry data (dFtave) is calculated inconsideration of the contribution (DVK) corresponding to the distanceinformation and distance precision, in addition to the first and secondphotometry data, thereby controlling the main emission amount. This canprevent underexposure or overexposure caused by adjusting exposure to ahigh- or low-reflectance region even when the principal object is whiteor wears a black dress. In other words, proper strobe lightphotographing which is almost free from the influence of the objectreflectance and an autofocus detection error can be achieved.

[0113] In the above embodiment, the contribution is obtained inaccordance with the distance information and distance precision. Evenwhen the contribution is obtained from only the distance information,more preferable strobe light photographing than the prior art can beperformed. However, a more preferable result can be attained usingprecision information, like the above embodiment.

[0114] Whether the difference between the third photometry data (dFtave)and the first photometry data (dFave) is equal to or smaller than apredetermined value (e.g., 0.5 (=class 2)) is determined. If so, theflow directly advances to step #126 without employing the thirdphotometry value (dFtave) which considers the contribution calculatedfrom the distance information. Also in terms of this, strobe lightphotographing hardly suffers an autofocus detection error.

[0115] According to the above embodiment, the strobe light photographingsystem comprises a means (distance encoder 18, brush 19, and lensmicrocomputer 112) for detecting object distance information from theposition of the focusing lens 12, a means (steps #111 to #117 in FIG. 6)for determining the precision of the detected distance information, ameans (step #121 in FIG. 6) for calculating a proper photometry levelLVL1 from the distance information, a means (step #121 in FIG. 6) forcalculating an identification level LVL2 for identifying an abnormalreflection region on the basis of the proper photometry level LVL1 andthe distance precision (distance range precision in step #119 in FIG. 6)set in accordance with the determination result of the distanceprecision, and a means (step #121 in FIG. 6) for comparing thephotometry values of a plurality of regions (more specifically, lightadjustment regions in FIG. 3) with the identification level LVL2 todetermine an abnormal reflection region out of the plurality of regions.The main emission amount is controlled to perform strobe lightphotographing by the photometry values dF of reflected object light inthe plurality of regions from which the abnormal reflection region isexcluded (#124 in FIG. 6).

[0116] Strobe light photographing is executed at photometry valuesobtained from a plurality of regions from which an abnormal reflectionregion is excluded, preventing underexposure of the principal object dueto the abnormal reflection region. That is, optimal strobe lightemission control corresponding to the precision of distance informationcan be performed regardless of a lens having low distance informationprecision, or a short-focus lens through which the precision decreasesas the object distance becomes longer.

[0117] The present invention can be applied to a system constituted by aplurality of devices, or to an apparatus comprising a single device.Furthermore, it goes without saying that the invention is applicablealso to a case where the object of the invention is attained bysupplying a program to a system or apparatus.

[0118] As many apparently widely different embodiments of the presentinvention can be made without departing from the spirit and scopethereof, it is to be understood that the invention is not limited to thespecific embodiments thereof except as defined in the appended claims.

What is claimed is:
 1. A system which includes a camera body, an interchangeable lens mounted on the camera body, and a strobe light mounted on the camera body, and performs preliminary emission before main emission in strobe light photographing, comprising: a unit which has a plurality of regions for splitting a field into a plurality of fields and performing photometry, and measures light reflected by an object to be photographed by preliminary emission in the plurality of regions; a unit which detects distance information of the object from a position of a focusing lens; a unit which determines precision of the distance information; a unit which calculates a proper photometry level from the distance information; a unit which calculates an identification level for identifying an abnormal reflection region on the basis of the proper photometry level and a distance precision set in accordance with a determination result of the precision; a unit which compares photometry values of the plurality of regions or light adjustment regions out of the plurality of regions with the identification level, thereby determining an abnormal reflection region; and a unit which controls an main emission amount by photometry values of reflected object light in the plurality of regions or the light adjustment regions out of the plurality of regions from which the abnormal reflection region is excluded.
 2. The system according to claim 1, wherein said unit which determines the distance precision determines the distance precision in accordance with identification data stored in the interchangeable lens.
 3. The system according to claim 1, wherein said unit which determines the distance precision determines the distance precision in accordance with an information signal corresponding to the distance precision of the interchangeable lens, and is arranged in the camera body.
 4. The system according to claim 1, wherein said unit which determines the distance precision determines the distance precision in accordance with individual lens information of the interchangeable lens, and is arranged in the camera body.
 5. The system according to claim 1, wherein said unit which determines the distance precision determines the distance precision on the basis of a ratio of upper and lower limit values of distance information data of the interchangeable lens, and is arranged in the camera body.
 6. A camera which controls a strobe light to execute preliminary emission before main emission, comprising: a unit which has a plurality of regions for splitting a field into a plurality of fields and performing photometry of light reflected by an object to be photographed by preliminary emission in the plurality of regions; a unit which determines precision of a distance information from a interchangeable lens mounted on the camera body; a unit which calculates a proper photometry level from the distance information; a unit which calculates an identification level for identifying an abnormal reflection region on the basis of the proper photometry level and a distance precision set in accordance with a determination result of the precision; a unit which compares photometry values of the plurality of regions out of the plurality of regions with the identification level, thereby determining an abnormal reflection region; a unit which measures a photometry values of reflected object light in the plurality of regions out of the plurality of regions from which the abnormal reflection region is excluded; and a unit which controls an main emission amount by the photometry values of reflected object light.
 7. The camera according to claim 6, wherein said unit which determines the distance precision determines the distance precision in accordance with identification data stored in the interchangeable lens.
 8. The camera according to claim 6, wherein said unit which determines the distance precision determines the distance precision in accordance with an information signal corresponding to the distance precision of the interchangeable lens.
 9. The camera according to claim 6, wherein said unit which determines the distance precision determines the distance precision in accordance with individual lens information of the interchangeable lens.
 10. The camera according to claim 6, wherein said unit which determines the distance precision determines the distance precision on the basis of a ratio of upper and lower limit values of distance information data of the interchangeable lens.
 11. A method for controlling a strobe light to execute preliminary emission before main emission, comprising the steps of: performing photometry by splitting light reflected by an object to be photographed by preliminary emission into a plurality of regions; determining precision of a distance information from a interchangeable lens mounted on a camera body; calculating a proper photometry level from the distance information; calculating an identification level for identifying an abnormal reflection region on the basis of the proper photometry level and a distance precision set in accordance with a determination result of the precision; comparing photometry values of the plurality of regions out of the plurality of regions with the identification level, thereby determining an abnormal reflection region; measuring a photometry values of reflected object light in the plurality of regions out of the plurality of regions from which the abnormal reflection region is excluded; and controlling an main emission amount by the photometry values of reflected object light.
 12. The method according to claim 11, wherein the step of determining the distance precision comprising the step of determining the distance precision in accordance with identification data stored in the interchangeable lens.
 13. The method according to claim 11, wherein the step of determining the distance precision comprising the step of determining the distance precision in accordance with an information signal corresponding to the distance precision of the interchangeable lens.
 14. The method according to claim 11, wherein the step of determining the distance precision comprising the step of determining the distance precision in accordance with individual lens information of the interchangeable lens.
 15. The method according to claim 11, wherein the step of determining the distance precision comprising the step of determining the distance precision on the basis of a ratio of upper and lower limit values of distance information data of the interchangeable lens. 